ISSN:1051-0761    

DOI:10.2307/1941904

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

Ecological phenomena are evident over a broad spectrum of space and time scales. Ecotones, being defined as zones of transition between adjacent ecological systems, also must occur over an equally broad spectrum of space and time scales. Scale—dependent constraints influence ecological phenomena and resulting zones of transition; however, in traditional ecotone studies little treatment has been given to these influences. This paper addresses aspects of the ecotone concept that relate to the strength of interactions between adjacent systems for a hierarchy of ecotones in a biome transition area in central New Mexico on the Sevilleta National Wildlife Refuge. Zones of transition occur at plant, population, patch, landscape, and biome levels in the hierarchy suggested here. Constraints differ across this hierarchy, primarily because of the different scales at which these constraints exert their influences. The basic strategy to understand these cross—scale influences must be to perform studies at different scales, and a hierarchical approach identifies those scales. This also is important for identifying the appropriate technologies that focus at the scales where transition zones between ecological systems/phenomena are expressed. A broad array of technologies are available for integrating the pattern–process relationships that occur across the many scales in ecological systems.

ISSN:1051-0761    

DOI:10.2307/1941905

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

Complex chains of mutual causation in human—environment relations may be analyzed by tracing past human interaction with the environment at the global, regional, and local scales. Historical analogues can be effectively employed to model the range of potential climate anywhere in the world. Their advantages include the use of actual regional airmass, hydrology, pedology, topography, and species distributional data, in addition to archaeology, documents, and ethnography. Of mediating importance are regions and landscapes, which manifest past and present human—environment relations and focus practical contemporary questions. The shifting position of ecotones is a convenient temporal and spatial marker of inclusive ecosystemic change. Ongoing research in Burgundy (France) is offered as an example.

ISSN:1051-0761    

DOI:10.2307/1941906

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

Accurate prediction of the ecological impacts of climatic change is a pressing challenge to the science of ecology. The current state of the art for broad—scale estimates of change in biomes and ecotones between biomes is limited to equilibrium estimates of ecological change under some future equilibrium climate. Uncertainties in these estimates abound, ranging from uncertainties in future climate scenarios to uncertainties in our ecological models and finally to uncertainties in modelling the feedbacks between the climate and the biosphere. Ecologists and policymakers need to go beyond equilibrium estimates of biosphere change to transient responses of the biosphere as the climate changes. Ecotones between biomes have been suggested as sensitive areas of change that could be effectively modelled and monitored for future change. Ecotones are also important in influencing local and regional biodiversity patterns and ecological flows. The ecological processes that could affect change at ecotones and within biomes are discussed; they include internal ecosystem processes, such as competition, and external abiotic processes, most notably drought and related disturbances. Drought followed by infestations and fire appears to be the most likely process that could mediate ecological change under a rapidly changing climate. The impacts would be apparent all across biomes, not just at ecotones. However, specific predictions about the dynamics of ecotones can be made qualitatively, based on a theory of patch scaling and diversity in relation to abiotic stressors. Under current conditions, the size of homogeneous patches is expected to be small at ecotones, but to enlarge with distance from the ecotone. Directional climatic change should promote a coalescence of patches on one side of the ecotone and increased fragmentation on the other side. Ecotones should begin to blur as viewed from a satellite only to re—form at some later date in a new location. This view is in contrast to the notion that ecotones would retain sharp distinction and simply move across the landscape. These changes are presented as hypotheses based on theory and should be testable in a mechanistic modeling framework that is only now being developed.

ISSN:1051-0761    

DOI:10.2307/1941907

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

It has been suggested that global climatic change may be detected by monitoring the positions of ecotones. I built a model of the dynamics of ecotones similar to those found in altitudinal or latitudinal treelines, where a slow tendency for the ecotone to advance is counterbalanced by disturbances such as fire or landslides. The model showed that the response of such ecotones to a wide range of simulated climate changes was slow and that the ecotone front was dissected. It would appear that such ecotones would not make suitable sites for monitoring climate change.

ISSN:1051-0761    

DOI:10.2307/1941908

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

A published correlative model has predicted that the distributional limits of plants and vegetation zones on mountains will increase in altitude with global warming. I test this hypothesis using results from published experimental studies. Investigations and models of the responses of leaf growth to temperature are in accord with the prediction. However, the individualistic responses of species to CO2enrichment indicate that the prediction is unlikely to be true for all species: growth is stimulated by CO2enrichment for some species but not for others. Wind speed generally increases with altitude on mountains, and plants from high altitude tend to be more wind resistant than species from the lowland. Therefore it is expected that, particularly on wind—swept mountains, global warming will not necessarily be followed by the spread of lowland species into the uplands.

ISSN:1051-0761    

DOI:10.2307/1941909

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

Soil biological parameters (e.g., Collembola), soil types, soil chemical parameters (pH, humus substances), and plant communities were studied in different ecosystems and ecotones in alpine, subalpine, and spruce forest zones in the Tatra National Park, Slovak Republic. The preliminary, selected data, based on a long—term research program, showed a high sensitivity of some alpine ecotones and ecosystems to long—distance transported acid deposits. The changes in different ecosystem parameters since 1977 were more extensive in alpine grasslands on limestone than on granite. The greatest soil pH decrease was in the plant communities Festucetum versicoloris (—1.5 pH), Geranio—Alchemilletum crinitae (—1.32 pH), and Saxifragetum perdurantis (—1.25 pH), which are restricted to places with snow accumulation and water runoff gullies. In these ecosystems the greatest changes occurred in the leaching of humus substances. Some formerly less abundant and rare soil animals restricted to acid bedrock became dominant in some ecosystems on limestone as well as on granite; other formerly dominant species disappeared from the entire study area (e.g., Folsomia alpina). The aerial extent of some ecosystems changed substantially since 1977, and their surrounding ecotones moved into the space formerly occupied by one of the adjacent ecosystems. These changes are detectable by remote—sensing methods. In Central European mountains, strongly affected by global and regional industrial air pollution (e.g., Krusne Hory, Krkonose, Beskydy), spruce forests started to die back from higher to lower mountain elevations. The effects of air pollution on alpine and subalpine vegetation were not studied there. Strong alterations in alpine ecosystems and ecotones were detected by the author during long—term studies in the High Tatra Mountains, and I suggest that subalpine and mountain forest belts will be affected here in the near future as they were in the more polluted Central European mountains. The ecosystems and ecotones in higher alpine zones are likely to be affected earlier than the ecosystems at lower altitudes. Detection of ecosystem alteration in the alpine zone may be used for prediction of acidification processes and global change in ecosystems at lower altitudes. The consequences of global climate change are predictable by monitoring changes in the extent of some ecosystems located in discrete mountain geomorphological units (e.g., karstic sinkholes, water runoff gullies, wind shadows, ridges exposed to wind, etc.) and ecotones among them because of their dependence on duration of snow cover, water supply, wind and frost exposure, and other abiotic and biotic factors.

ISSN:1051-0761    

DOI:10.2307/1941910

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

In California, a number of studies on the interaction between shrubs (Baccharis pilularis) and herbaceous species in annual grasslands have led to the proposal of a conceptual functional model for the dynamics of ecotones between species patches. In our study Chile we used a similar shrub (Baccharis linearis) and annual grassland species to test the robustness of the hypothesis that ecotones between similar landscape elements under similar climate constraints also have similar dynamics. The herbaceous and shrubby ecotone vegetation was described using cover measurements along the same transects in aerial photographs of 1955, 1962, and 1980, and in the field in 1987. The herbaceous species were then determined and quantified by their mass on both sides of the ecotone. Colonization capacity of B. linearis was estimated by describing its establishment on perturbed sites and estimating its seed dispersion. Field and laboratory experiments evaluated the effect of herbaceous species on shrubs at seedling stages. We found similarities between the Chilean and California dynamics in the strong inhibition posed by the annual herbaceous strata to shrub colonization. In Chile this inhibition results in little or no shrub invasion for at least three decades. We also found, just as in California, a reduction of the herbaceous biomass under the shrub canoies, once these get established. However, in Chile, grassland species under the canopy of Baccharis shrubs have a higher biomass and relatively higher species diversity than in California. This difference is related to the fact that herbivores and especially leporids, which in Chile are introduced, play completely different roles in the two regions. In California, herbivores, including leporids, tend to be restricted to areas under the shrub canopies and consequently remove most of the grasses under the shrubs, whereas in Chile leporids are not restricted to shrub patches and the total herbivore effect on forbs under and around shrub patches is much smaller. Consequently, in Chile there is no facilitation of shrub invasion due to herbaceous plant removal by herbivores, and the ecotone is less mobile than in California. The 30—yr stability of the ecotone between Baccharis and grassland shown by our data seems to support this proposition. Our results also suggest that the most abundant species of annual grass in California (Bromus mollis), highly influential in the inhibition of Baccharis colonization, does not behave in a comparable way to its Chilelean congener Bromus berterianus, mainly because it germinates and emerges later in the season than Baccharis linearis. In the Chilean case, herbs such as Erodium cicutarian and Trifolium species seem to be more influential on shrub seedling survival. We conclude that in spite of the strong climatic, physiognomic, and taxonomic similarities between the two areas, ecotones in analogous patches are only partially similar. Consequently, eventually management extrapolations between these regions should be done with extreme care. More generally, our study suggests that extrapolation of management decisions between similar regions, even as similar as chaparral—matorral ecosystems, should be postponed until shown that analogous elements really play sufficiently similar roles in the different areas.

ISSN:1051-0761    

DOI:10.2307/1941911

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

The spatial and temporal distribution of sediment, nutrients, and cations in a 2—ha wetland near Shawano, Wisconsin (USA) was used to evaluate the effect of wetland ecotones on water— and windborne fluxes at ecosystem and landscape scales. Within the wetland ecosystem the ecotones studied were beach ridges deposited by post—glacial White Clay Lake, and stream levees deposited by a second—order stream flowing through the wetland. Snow, soil, and surface water data collected from a 52—point sampling grid were geostatistically analyzed to derive contour plots of within—wetland concentrations. Wind—blown snow form the frozen lake surface accumulated in the wetland behind a low beach ridge to a depth of>65 cm, nearly 7 times the depth at wind—protected areas of the wetland. As a result of this snow accumulation, areas to the lee of the beach ridge annually received 10% more water and 1.5% more inorganic N from direct precipitation than did other areas of the watershed. The use of geostatistical plots to analyze wetland surface waters revealed that: (1) within—wetland spatial variability was high on every sampling date except early snowmelt; (2) on a given sampling date, concentration patterns differed for different elements, sometimes substantially; (3) with the exception of NO3—N, the spatial patterns for a given material changed considerably over time; and (4) many of these spatial patterns were interpretable on the basis of observed water flow patterns and wetland ecology. In general, there was a decrease in the concentrations of inorganic solids and most ions, and an increase in Ca++and chemical oxygen demand with distance from the stream. Overbank fluxes contributed P to the wetland during spring and fall floods, but diluted ambient P concentrations during snowmelt events. During snow—free periods there was a sharp gradient in NO3—N concentrations from a streamside value of °5 mg/L to45 m from the stream. Measurement of the concentration gradient perpendicular to the stream indicated NO3—N disappearance rates of 6.6 g/100 m of distance during the spring flood. Soil concentrations of mineral matter and P were highest in areas of the wetland closest to the stream; soil concentrations of ammonium and nitrate were spatially disaggregated, and related to levee elevation. At the watershed scale the wetland retained and/or denitrified 15.2% of the total solids, 13.7% of the N, and 14.2% of the P fluxes from the watershed, thus benefitting the water quality of White Clay Lake.

ISSN:1051-0761    

DOI:10.2307/1941912

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY

摘要:

The paper discusses how variability of river margins interacts with riparian function at the landscape level, in order to develop inferences about the future of this interaction with respect to potential effects of a global climatic change. A riparian approach to the ecology of river landscapes should be useful in that it offers an opportunity to improve our understanding and management of the effects of environmental change at the ecosystem level.

ISSN:1051-0761    

DOI:10.2307/1941913

出版商:Ecological Society of America    

年代:1993

数据来源: WILEY